Transmission and reception of intelligence



Patented Sept. 20, 1938 i UNITED STATES PATENT OFFICE TRANSMISSION AND RECEPTION OF INTELLIGENCE Samuel G. Frantz and Brunson S. McCutchen,

Princeton, N. J., assignors to Radio Corporation of America, a corporation of Delaware Original application April 23, 1935, Serial No. 17,775. Divided and this application April 17, 1963, Serial No. 74,834

7 Claims. (01. 179-1) This invention relates generally to the transmeans are provid to re-eXpend the intensity mission and reception of intelligence and is sperange to t existing in the Original signalcifically directed towards improving the quality These means at the receiver must be so arranged of the received intelligence. as to work in correspondence with the compres- The present application is a division of copendsion effected at the transmission station. 5 ing application Serial Number 17,775 filed April At this point we desire to emphasize thefact 23, 1935, entitled Transmission and reception of that one of the benefits that will be derived from intelligence which in turn is a continuation in the use of our system will be the lessening of part of application Serial Number 496,595 now the effect of atmospheric disturbances p the 10 U. S. Patent No. 2,006,989. receiver. I 10 More specifically, the present invention relates The measure of the efiect of atmospheric to systems and methods for maintaining the reurbances or other interference on'the quality of lations between the various increments of the inreception s the ratio of interference nt nsity t telligence issuing from an electrical energy transsignal s y, and this efieet Will therefore latin device at a receiving point substantially m t pronounced wh h si nal inten ity is 15 proportional to the relations between the various low. W e present te dur n weak ori corresponding increments of the original intelliinal s s, t transmitted signal intensity Will ealways be greater than it would be were there no An object of the invention is to provide a novel mp si n f n en i y range b f r tr sm -.:o and efiicient method of transmission and recepsion, and therefore the ffect f interfer nce i tion of signals. minimized. In other words, when weak signals Another object of the present invention is the are being transm t the energy W be more achieving of clear fidelity of reproduction at the amplified before it is used for modulation with receiving end of radio signals and in particular the result that ordinary atmospheric disturb- -3 music, by partial or total compression of the inances will not obscure the signal. 5 tensity range, or range of modulation at the This invention relates to and comprises the transmitting end and corresponding expansion of above described compression and expansion of the intensity range at-the receiving end. intensity range, and means for accomplishing the In the proposed system the degree or percentcompression and expansion. age of modulation applied to the carrier wave at In applicants parent applications there are 30 the transmitting end instead of being made di- P D S for this purpose three y of informy proportional to the intensity of the signal ing the receiving apparatus as to what amount of in the microphone circuit is made to sufier a expansion is necessary. The three cases may be smaller percentage variation than the latter. classified as follows:

This may be called range compression or sub- 1. Separate wire or radio channel. 35

proportional modulation. Thus, in this system 2. Variation of carrier frequency. a weak signal 'will be more amplified before it is 3. The use of the residual variation of moduused for modulation than will a strong signal. A lation percentage i elf s h si nal which comfeature of our invention is then that the intensity municetes t0 the receiving apparatus ow much 40 range or the ratio between maximum and minlthe signal should be p fi 40 mum percentage of modulation of the transmit- The simplest case of the latter would be loga- Y ted radio signal is less than the intensity ran e of rithmic sub-proportional range compression at the original signal. The extent or degree of this the transmitter wlth corresponding logarithmic compression of intensity range may in practice super-proportional range expansion at the reresult in about the same ratio of maximum to ceiver. Expressed mathematically we have:- 45

minimum percentage of modulation as is at pres- 1 ent obtained by manual control at broadcasting 3 stations; or, the compression may be carried much further even to the limit at which there is f 2 2 f 1 2 1 a total obliteration of intensity range and the Where I1=r1g1na1 Intensity 50 Iz=transmitted intensity of modulation signal is transmitted at constant percentage I3=rece1ver output intensity modulation. In general, in the present system I the intensity range will be compressed but not 751 and 752 are constants obliter t d, and a=a constant 1 At the receiving end of the present system Inusingthe system described in the third sub- 55 division it is obvious, of course, that the intensity range must not be completely obliterated.

An object of the present invention is to provide a specially constructed bridge arran e ent for effecting the desired compression at the transmitter and expansion at the receiver.

Another object of the invention is the provision of a plurality of said specially constructed resistance bridges arranged in cascade.

Still other objects of the invention will be apparent from the following description of typical circuits according to our invention illustrated in the accompanying drawing, in which Figure 1 illustrates a transmitter arrangement of one form of our invention utilizing a so-called temperature bridge;

Figure 2 illustrates diagrammatically a method by which two or more temperature bridges may be cascaded; and,

Figure 3 illustrates diagrammatically a receiver in accordance with our invention employing a temperature bridge arrangement for receiving an appropriately expanding signal transmitted from a system such as shown in Figure 1.

Referring to Figure 1 a microphone circuit is shown composed of microphone 5, transformer I and the usual source of current 6. An amplifier for the current generated in the microphone circuit is shown generally at 8 coupled to the microphone circuit by means of the transformer 1. The output of the amplifier 8 is connected to a temperature bridge 9 by means of conductors l3 and I2 connected to diagonally opposite points l4 and I5 respectively of the bridge 9. The other two diagonally opposite points of the bridge 9, namely, i6 and H are connected by conductors II and I0 respectively, to a modulator and radio frequency energy source circuit of any well known design. Referring more particularly to the temperature bridge I, 2, 3 and 4 compose the four elements thereof. Elements and 4 are of the same material and elements 2 and 3 are of some other material having a different temperature coefficient of resistance than said first material. The wires it will be evident are appreciably heated by the passage of the currents due to the signal voltage applied from the amplifier output. With maximum signal voltage the bridge is hottest and the resistances are so proportioned that under this condition the bridge is almost balanced; that is, the ratio of bridge output voltage to bridge input voltage is a minimum. .With very low input voltage the bridge is comparatively cold and has a maximum of unbalance and hence the ratio of output to input voltage is a maximum. Thus the bridge acts as a non-proportional attenuator, attenuating strong signals more than weak ones. While we do not intend to limit ourselves to any particular construction of the bridge one way in which the bridge could be constructed would be of small wires about the size of flash-light bulb filaments. Either I and 4 or 2 and 3 may be resistances so designed as to heat but little. Broadly, the term temperature bridge as used herein includes any network with input and output connections in which the ratio of output to input voltage varies according to the input voltage as a result of change of resistance of any of the elements of the network due to heating by the current passing through it.

In Figure 1 the arrangement could be such that the elements I and 4 have comparatively high temperature coefficient of resistance and elements 2 and 3 comparatively low temperature coeflicient of resistance.

Attention is now directed to Figure 2. In said figure conductors l2 and I3 correspond to the conductors l2 and I3 leading from the output of the amplifier 8 of Figure 1. Conductors I2 and I3 are connected to diagonally opposite points 2| and 20 respectively of the temperature bridge l8. I'he other two diagonally opposite points 22 and 23 of the bridge l8 are connected by conductors 24 and 25 respectively to two diagonally opposite points 21 and 26 respectively of a second temperature bridge device I9. The other two points of said last named bridge, namely, 28 and 29 may be connected either to another similar bridge arrangement or to the modulator and radio frequency energy source as shown by Figure 1 through the medium of conductors Ill and II. It will thus be evident that in the arrangement shown any number of temperature bridges may be connected in cascade for obtaining any results desired.

Attention is now directed to Figure 3 which shows a receiver adapted to properly expand the signals which were compressed by the transmitter shown in Figure 1. In Figure 3, 3|! represents generally a stage of audio frequency amplification in an ordinary radio receiver. Conpled to the output of said stage by means of transformer 3| is a temperature bridge 32 in accordance with our invention. It will be noted that the secondary of the transformer 3| is connected by conductors 33 and 45 to two diagonally opposite points of said bridge 32. The other two diagonally opposite points of the bridge are connected by means of conductors 35 and 36 to the input of an amplifier generally shown at 31. The output of this amplifier 31 is connected by means of conductors 39 and 38 to a receiving instrument shown generally as a telephone receiver 40. The bridge 32 is made up of elements I, 2, 3 and 4 which operate in a somewhat similar manner to that described above in connection with Figure 1 except that in the case of the receiver, the bridge will be in approximate balance for minimum signal, so that in Figure 3 the greater the applied electromotive force across the secondary of the transformer 3| the greater will be the resistance of elements I and 4 compared to the resistance of elements 2 and 3. This condition causes an increased unbalance of the bridge and an increased output current. It is to be distinctly understood that while we have shown only one bridge arrangement in the receiver shown in Figure 3 two or more such bridge arrangements may be arranged in cascade as shown in Figure 2.

We claim:

1. In a radio receiving system including means for connecting the input of the system to a source of variable intensity signal energy and means for connecting the output of the system to a utilizing circuit, a four-arm resistance bridge interposed between said two means, opposite arms of said bridge being constructed so as to have substantially the same temperature coefficient of resistance but one pair of said arms having different temperature coefficient of resistance than the other thereof, said bridge being adjusted so as to be approximately balanced for minimum signal intensity and to become more and more unbalanced as the average intensity of the signal energy increases, the ratio of output to input voltage varying according to the input voltage as a result of change of resistance of any of the elements of the network due to heating by current passing therethrough.

2. In a radio communication system, a source of variable intensity signal voltage and a utilizing circuit, a four-arm resistance bridge, a pair of diagonally opposite terminals of said bridge comprising input terminals therefor, the other pair of diagonally opposite terminals of the bridge comprising output terminals therefor, means for connecting the source of signal voltage between the input terminals of the bridge and means connecting the utilizing circuit between the output terminals of the bridge, each of a pair of opposite arms of said bridge including means having a, high temperature coefficient'of resistance, the other pair of opposite arms including means having a comparatively low temperature coefiicient of resistance, said bridge being adjusted so as to be approximately in a balanced condition for a predetermined value of average signal voltage and to become more and more unbalanced as the average intensity of the signal voltage departs from said value in one direction, the ratio of output to input voltage of said bridge circuit varying according to the average value of signal voltage as the result of change of resistance of any of the means provided in the arms of said resistance bridge due to heating by current passing therethrough.

3. In a radio communication system, a source of variable intensity signal energy and a utilizing circuit, a four-arm resistance bridge interposed between said source and the utilizing circuit, opposite arms of said bridge including means having substantially the same temperature coefficient of resistance but the means provided for one pair of said arms having different temperature coemcient of resistance than the other pair thereof, said bridge being adjusted so as to be approximately in a balanced condition for a predetermined average value of signal intensity and to become more and more unbalanced as the average intensity of the signal energy departs from said value, the'ratio of output to input voltage of said bridge circuit varying according to the input voltage as the result of change of resistance of any of the elements of the network due to heating thereof by current passing therethrough.

4. In a radio communication system, a source of variable intensity signal energy and a utilizing circuit, a four-arm resistance bridge circuit interposed between said source and the utilizing circuit, opposite arms of said bridge including means having substantially the same temperature coefiicient of resistance but the means provided for one pair of said arms having difierent temperature coefiicient of resistance than the means provided for the other pair of arms,,said bridge being adjusted so as to be approximately in a balanced condition for substantially maximum average value of signal intensity and to become more and more unbalanced as the average intensity of the signal energy decreases, the ratio of output to input voltage of said bridge circuit varying according to the input voltage as the result of changes in the resistance of any of the elements of the bridge circuit due to heating thereof by current passing therethrough.

5. A volume range compressor comprising a resistance bridge having input terminals and output terminals, means for connecting a source of varying intensity voltage to said input terminals, a utilizing circuit connected to said output terminals, means connected in the arms of said bridge for attenuating electrical energy applied to the input terminals thereof to a greater or less extent depending upon the average intensity of the electrical energy applied to the input terminals of the bridge, said means attenuating high intensity energy to a greater extent than low intensity energy whereby the ratio between the lowest average intensity of the energy applied to the input of the bridge to the highest average intensity applied thereat is substantially greater than the ratio of the lowest average intensity of the voltage appearing across the output terminals of the bridge to the highest average intensity voltage applied thereat.

6. A volume range expander comprising a resistance bridge having' input terminals and output terminals, means for connecting a source of varying intensity electrical energy to said input terminals, 3, utilizing circuit connected to said output terminals, said bridge including means for attenuating electrical energy applied to the input terminals thereof to a greater or less extent depending upon the average intensity of the electrical energy applied to the input terminals of the source, said means acting to attenuate high average intensity energy less than low average intensity energy, whereby the ratio between'the lowest average intensity energy applied to the input terminals of the bridge and the highest average intensity applied thereat is substantially smaller than the ratio of the lowest average intensity energy appearing across the output terminals of the bridge andthe highest average intensity energy applied thereat.

7. A volume range expander device comprising, a four-arm bridge circuit, substantially equal fixed resistance means having'a low temperature coeflicient of resistance connected in each of two opposite arms of the bridge and substantially similar resistance means having a high temperature coefilcient of resistance connected in each of the other two opposite arms of the bridge.

SAMUEL G. FRANTZ. BRUNSON S. MCCUTCHEN. 

